1. Field of the Invention
This invention concerns an oil recovery process, and more specifically is concerned with a surfactant oil recovery process. Still more specifically, this invention is concerned with an oil recovery process using a surfactant or a combination of surfactants which is operable for surfactant flooding purposes in formations whose temperature are from 70.degree.-300.degree. F and which formations contain high salinity and/or high divalent ion concentrations of water, and a method of formulating and injecting the fluid so as to avoid phase instability.
2. Description of the Prior Art
Petroleum is normally recovered from subterranean formations in which it has accumulated by penetrating the formation with one or more wells and pumping or permitting the petroleum to flow to the surface through these wells. Recovery of petroleum from formations is possible only if there is an adequate concentration of petroleum in the formation and if there is sufficient permeability or interconnected flow channels in the formation to permit the flow of fluids therethrough if sufficient pressure is applied to the fluids. When the formation has natural energy present therein in the form of an underlying active water drive, or gas dissolved in the petroleum which can exert pressure to drive the petroleum to the producing well, or a high pressure gas cap above the petroleum within the formation, this natural energy may be utilized to recover petroleum. Recovery by utilization of natural energy is referred to as primary recovery. When this natural energy source is depleted or in the instances of formations which do not contain sufficient natural energy initially to support primary recovery, some form of supplemental or enhanced recovery process must be applied to the formation in order to extract additional petroleum therefrom. Supplemental recovery is sometimes referred to in the art as secondary or tertiary recovery, although in fact it may be primary, secondary or tertiary in sequence of employment.
Waterflooding, involving the injection of water into the subterranean, petroliferous formation for the purpose of displacing petroleum toward the producing well, is the most economical and widely practiced supplemental recovery method. Water does not displace petroleum efficiently, since water and oil are immiscible and the interfacial tension between water and oil is quite high. Persons skilled in the art of oil recovery have recognized this weakness of waterflooding and many additives have been described in the literature for decreasing the interfacial tension between the injection water and the formation petroleum. The use of petroleum sulfonates in oil recovery processes is described in many prior art references including U.S. Pat. No. 3,302,703.
Many prior art references also disclose the use of combinations of surfactants for use in formations containing water having high salinities and/or high concentrations of divalent ions. Included in these are U.S. Pat. Nos. 3,792,731; 3,811,504; 3,811,505; and 3,811,507, which describe mixtures of anionic and nonionic surfactants especially useful in formations containing water of high salinity or having high concentrations of divalent ions including calcium and magnesium dissolved therein. U.S. Pat. No. 3,508,612 describes an oil recovery process using a mixture of an organic sulfonate such as a petroleum sulfonate and a sulfated, polyalkoxylated (especially ethoxylated) hydrocarbon for use in high salinity formations. U.S. Pat. Nos. 3,827,497 and 3,890,329 describe oil recovery fluids and processes employing a mixture of an organic sulfonate such as a petroleum sulfonate and a sulfonated, ethoxylated hydrocarbon surfactant. U.S. Pat. No. 3,977,497 describes an oil recovery process employing an alkylarylpolyalkoxyalkyl sulfonate as the sole surfactant in a fluid for recovering petroleum from high salinity, high temperature formations.
Despite the substantial amount of art discussed above dealing with the use of surfactant fluids for oil recovery purposes, a commercially viable surfactant flooding oil recovery process suitable for use in high temperature, high salinity formations has not yet been developed. Oil recovery processes employing the alkylpolyalkoxyalkyl sulfonates or alkylarylpolyalkoxyalkyl sulfonates such as an alkylpolyethoxyethyl sulfonate or an alkylarylpolyethoxyethyl sulfonate show great promise because these materials are both temperature stable and adaptable to high salinity, high divalent ion containing formation waters. An aqueous solution of some of these surfactants have, however, been found to exhibit phase instability and injection of a phase-unstable surfactant solution into a formation is at best ineffective for oil recovery purposes and is potentially hazardous because of the possibility of plugging small capillary flow channels of the formation with insoluble organic material.
In view of the foregoing discussion, it can be appreciated there is a substantial present economic and commercial need for a surfactant flooding oil recovery process suitable for use in high temperature, high salinity water-containing oil formations.